the invention relates to a process and apparatus for delivery of a liquid under pressure. More particularly, but not by way of limitation, the liquid may be water pumped from a well or other source for delivery to residential or commercial users.
In common private water systems, water is pumped from a well to a pressure tank which is designed to maintain a supply of water under pressure for random usage patterns. The reason for the pressure tank is to eliminate the need for an elevated storage tank or the requirement for the pump to run continuously in order to instantly meet a demand for water.
Typical systems rely on compression of air in the tank to maintain pressure in the tank after the pump stops. The water pump introduces water into a closed tank compressing air in the tank until reaching a preset high pressure. A pressure operated switch disconnects the power to the pump at this pressure. After the water pump stops, water may be drawn from the tank under pressure of the compressed air. As water is removed from the tank, the air expands and the pressure drops until the pressure switch which controls the pump motor closes and starts the cycle again.
A problem with this type of system is the fact that some of the air is gradually dissolved into the water and must be replenished with either a venturi or bleeder valve arrangement. To make the system operate more efficiently, an air volume control is employed to manage the ratio of air to water in the tank. Another means of addressing the loss of air is to employ a diaphragm or bladder as a barrier between the air and water. The sealed air chamber may be precharged to a pressure which again adjusts the air to water ratio at given pressures for efficient operation.
The apparatus and process of prior art have several distinct disadvantages. First, if the pressure is increased on an installed system, the drawdown (volume of water that can be removed from the tank between cycles) is reduced. Since the drawdown volume is directly related to refill time, the pump may run for less than the manufacturer's recommended minimum run time and shorten the pump life. Second, the standard pressure switch differential is 20 PSI, and for many ordinary pressure switches the differential cannot be adjusted to half that or less; especially at higher pressures. Further, both type of systems currently in use are prone to a type of failure called water logging which causes the pump to cycle rapidly and often fail prematurely. In the case of standard hydropneumatic tanks a sticking air volume control valve or float causes an imbalance in the air to water ratio resulting in either rapid cycling or air being expelled into the water delivery lines. In the case of bladder or diaphragm tanks, the membrane separating the air from water is prone to perforation resulting in water logging. Also the precharge pressure in a diaphragm or bladder tank must be checked and adjusted at regular intervals in order to maintain proper air to water ratios.
There is a need for a system in which the drawdown volume does not vary when the operating pressure is adjusted, will permit a smaller differential in operating pressure, and will reliably maintain optimum air to water ratio.